Hello,
It's possible to click on the chart of coin types in the dashboard of "My coins" (except if you chose the "old" collection display). It leads to the list of your coins of that type. It was (briefly) announced here:
https://en.numista.com/forum/topic87462.html
The question about "white metal" was already raised here:
https://en.numista.com/forum/topic44590.html
When converting the metals into the new model, I observed that "white metal" has been mostly used to describe the light or silvery colour, not describing any specific alloy. I also observed "yellow metal" to be used for some coins.
I would prefer the "composition" field to describe only the material of the coins or tokens. If you know which alloy was used, you can select it in the dropdown list. "Tin-lead" or "zamac" for example already exist. If an alloy is not listed yet, you can select "Other". Whether it is listed or not, the "additional details" field allows to describe the exact composition (e.g. Sn 93%, Sb 3.5%, Cu 3.5%).